In case of polishing both sides of a semiconductor wafer, a carrier whose thickness is equal to that of a finished wafer is used to restrain subduction of polishing cloth while the polishing operation is performed, so that a mirror-surface wafer, which has superior flatness and whose outer edges are not rounded, can be produced.
However, when the thickness of the wafer reaches the finished thickness, the polishing cloth contacts the carrier. By the contact, the carrier is abraded and its thickness is reduced, so the carrier must be frequently exchanged. Of course, the abraded carrier cannot be reused. Further, when the thickness of the wafer reaches the finished thickness, the polishing cloth contacts the entire wafer and carrier, so abrasion resistance is increased. Therefore, a great load is applied to the polishing apparatus and a high power driving source is required.
A conventional technology for solving the above described problems is disclosed in Japanese Laid-open Publication No. 11-254305A. In this technology, a thickness adjusting member is provided to an edge part of a through-hole (a wafer holding hole) of a carrier so as to make a thickness of the edge part of the through-hole thicker than that of a main body part of the carrier. With this structure, the finished thickness of the wafer can be adjusted. Further, when the thickness adjusting member is abraded, it can be exchanged so that abrasion of the main body part of the carrier can be prevented and the above described problems can be solved.
However, in the above described conventional technology disclosed in the Japanese Laid-open Publication No. 11-254305, the thickness adjusting member is provided to the edge part of the through-hole. A thickness of the outer edge of the finished wafer, which is located just inside of the thickness adjusting member, must be thicker than the center part the finished wafer, and flatness of the finished wafer must be bad. Further, the outer edge of the wafer collides with an inner circumferential face of the through-hole of the carrier and is prone to be damaged.